RFR: 8290310: ChangeListener events are incorrect or misleading when a nested change occurs [v6]
danielpeintner
duke at openjdk.org
Wed Mar 5 18:27:30 UTC 2025
On Wed, 5 Mar 2025 18:06:26 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:
>> This provides and uses a new implementation of `ExpressionHelper`, called `ListenerManager` with improved semantics.
>>
>> # Behavior
>>
>> |Listener...|ExpressionHelper|ListenerManager|
>> |---|---|---|
>> |Invocation Order|In order they were registered, invalidation listeners always before change listeners|(unchanged)|
>> |Removal during Notification|All listeners present when notification started are notified, but excluded for any nested changes|Listeners are removed immediately regardless of nesting|
>> |Addition during Notification|Only listeners present when notification started are notified, but included for any nested changes|New listeners are never called during the current notification regardless of nesting|
>>
>> ## Nested notifications:
>>
>> | |ExpressionHelper|ListenerManager|
>> |---|---|---|
>> |Type|Depth first (call stack increases for each nested level)|(same)|
>> |# of Calls|Listeners * Depth (using incorrect old values)|Collapses nested changes, skipping non-changes|
>> |Vetoing Possible?|No|Yes|
>> |Old Value correctness|Only for listeners called before listeners making nested changes|Always|
>>
>> # Performance
>>
>> |Listener|ExpressionHelper|ListenerManager|
>> |---|---|---|
>> |Addition|Array based, append in empty slot, resize as needed|(same)|
>> |Removal|Array based, shift array, resize as needed|(same)|
>> |Addition during notification|Array is copied, removing collected WeakListeners in the process|Appended when notification finishes|
>> |Removal during notification|As above|Entry is `null`ed (to avoid moving elements in array that is being iterated)|
>> |Notification completion with changes|-|Null entries (and collected WeakListeners) are removed|
>> |Notifying Invalidation Listeners|1 ns each|(same)|
>> |Notifying Change Listeners|1 ns each (*)|2-3 ns each|
>>
>> (*) a simple for loop is close to optimal, but unfortunately does not provide correct old values
>>
>> # Memory Use
>>
>> Does not include alignment, and assumes a 32-bit VM or one that is using compressed oops.
>>
>> |Listener|ExpressionHelper|ListenerManager|OldValueCaching ListenerManager|
>> |---|---|---|---|
>> |No Listeners|none|none|none|
>> |Single InvalidationListener|16 bytes overhead|none|none|
>> |Single ChangeListener|20 bytes overhead|none|16 bytes overhead|
>> |Multiple listeners|57 + 4 per listener (excluding unused slots)|57 + 4 per listener (excluding unused slots)|61 + 4 per listener (excluding unused slots)|
>>
>> # About nested changes
>>
>> Nested changes are simply changes...
>
> John Hendrikx has updated the pull request incrementally with one additional commit since the last revision:
>
> Throw StackOverflowError if non-converging listener changes are detected
modules/javafx.base/src/main/java/com/sun/javafx/binding/ListenerList.java line 69:
> 67: * been notified in higher level loops, while deeper nesting levels
> 68: * communicate to higher level loops whether a nested notification
> 69: * actually occurred if if it completed normally or was aborted early.<p>
Suggestion:
* actually occurred if it completed normally or was aborted early.<p>
-------------
PR Review Comment: https://git.openjdk.org/jfx/pull/1081#discussion_r1981930914
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